There is no question that the most talked-about topic heading into the U.S. Open is Serena Williams' Grand Slam bid. Even if she does dominate the conversation, a certain ''Big Four'' of men's tennis will provide plenty to discuss, too, as usual.
No. 1-seeded Novak Djokovic, for example, has been nearly as dominant as Williams in 2015. He won the Australian Open, was the runner-up at the French Open, then won Wimbledon, part of a 56-5 season that includes six titles and 10 consecutive appearances in tournament finals.
Given his excellence on hard courts, it's hard to believe he's earned the trophy only once at Flushing Meadows.
Five-time U.S. Open winner Roger Federer is 34, hasn't won a Grand Slam championship in more than three years - and yet the No. 2-seeded Swiss star might just be as much of a threat as anyone to be in Arthur Ashe Stadium on the second Sunday. He made it all the way to the final at Wimbledon before losing to Djokovic, then beat the Serb for the hard-court Cincinnati Masters title this month.
''Still not very happy with my form and with my game,'' Djokovic said after that loss to Federer, ''but I have a week to work on it.''
No. 3 Andy Murray also defeated Djokovic in a hard-court final in August, at Montreal, and has made it to two semifinals and one final at this year's majors. Like Djokovic and Federer, he is a past U.S. Open champion.
Rafael Nadal is worth keeping an eye on for the simple reason that no one quite knows how well he'll play. He hardly has performed up to the standards that earned 14 Grand Slam titles, including two at the U.S. Open, and is seeded only No. 8. Nadal faces what could be a truly tough test in his opening match against 18-year-old Borna Coric. Get past that, then win three more matches, and Nadal could face Djokovic in the quarterfinals.
Here are other things to watch at the U.S. Open, which begins Monday in New York:
Maria Sharapova is a five-time major champion, including at the 2006 U.S. Open, but she's hardly match-ready. She hasn't competed since her semifinal loss to Williams at Wimbledon in July, sidelined since by an injured right leg. ''You always have to believe in the ability to go through the little things that you might have,'' Sharapova said. ''There's no athlete who's ever 100 percent healthy.''
KYRGIOS AND WAWRINKA
Murray's first-round opponent is Nick Kyrgios, a 20-year-old Australian who has been in the headlines for all the wrong reasons recently. During a match in August, a courtside microphone picked up Kyrgios telling his opponent, two-time major champion Stan Wawrinka, that another Australian player had slept with Wawrinka's girlfriend. Kyrgios was fined by the ATP - and is on probation for the next six months, with an additional fine and a 28-day suspension threatened. Both Kyrgios and Wawrinka will be dealing with that episode's fallout.
FEDERER'S NEW RETURN
Federer showed off a new, net-rushing, half-volley return in Cincinnati, so it will be interesting to see how much he uses that at the U.S. Open. ''I'll always mix it up,'' he said, ''and make it, I guess, uncomfortable for my opponent.''
Mardy Fish, a 32-year-old American once ranked in the top 10, will be playing the final tournament of his career after dealing with anxiety disorder, which forced him to withdraw from the 2012 U.S. Open. His first-round opponent is 102nd-ranked Marco Cecchinato of Italy, who has never played a Grand Slam match and is 0-6 in tour-level matches.
RAISING THE ROOF
Fans still have to sit out rain delays at Arthur Ashe Stadium for one more year, but they'll get a break from the sun. The framework to support a retractable roof has been installed above the tournament's main court, providing shade for part of the upper deck, which used to bake on hot days. The fully operational roof is scheduled to be in place for the 2016 U.S. Open. Four new video screens also have been added at Ashe, replacing the previous two.
AP Sports Writer Rachel Cohen in New York contributed to this report.